How do I get to know my real last name?

When my grandpa came here from Canada. He changed our last name. Is there a website or something that can help me find out what my real last name is on very little info? I don't wanna have to pay for anything. Last name is Anton but its been shortened from its French-Canadian parent. I think to say its original name is antonio-cha-chuck. I over heard my aunts talking about it and I wanted to know how to spell it correctly.